If i was doing the job i would also use a jig but slightly different, would make it with 2 holes with an L shape cross section, make all holes on the assembly the same pitch, so you would clamp the jig drill & tap first hole, shouldered bolt goes in that hole, do second hole, move jig down using the shouldered bolt in the second hole drill & tap third hole in so on, the jig can also be used on the clear holes.
Mike